The invention relates to a process for producing epoxy-functional silicones by a hydrosilation reaction between an SiH-functional silane or siloxane and an olefin epoxide, wherein gelation during processing, due to thermally-induced epoxide-mediated crosslinking is eliminated by use of certain rhodium or platinum sulfonium hydrosilation catalysts in combination with a tertiary amine stabilizer. The invention also relates to an epoxysilicone composition that is stable to epoxide-mediated crosslinking both during and after a hydrosilation reaction, as well as to a method for stabilizing olefin epoxides and epoxysilicones in the presence of a hydrosilation catalyst and SiH-functional group.
The hydrosilation reaction of unsaturated epoxides to SiH-functionalized silicone polymers has long been recognized as an elegant and convenient route to the manufacture of functionalized silicone materials. Epoxysilicone polymers are conveniently manufactured through the hydrosilation reaction between a SiH-functionalized silicone and olefin epoxide. The general hydrosilation reaction for silanes can be expressed as EQU .tbd.SiH+CH.sub.2 .dbd.CH--Q.fwdarw..tbd.Si--CH.sub.2 CH.sub.2 --Q
and the general hydrosilation reaction for siloxanes can be expressed as EQU --((H)(Q')SiO)--+CH.sub.2 .dbd.CH--Q.fwdarw.--((Q--CH.sub.2 --CH.sub.2)(Q')SiO)--
where Q and Q' represent an organic radical. These reactions, as well as hydrosilation reactions in general, are known to be catalyzed by platinum compounds. However, as disclosed in commonly assigned U.S. patent application Ser. No. 07/473,802, filed Feb. 2nd, 1990, it has become apparent that the same platinum reagents used in the catalysis of the hydrosilation reaction to generate heterocyclic epoxy-functionalized silicones also promotes a highly undesirable epoxy ring-opening reaction. This latter reaction results in crosslinking and premature gelling of an epoxysilicone in the presence of SiH groups and the platinum hydrosilation catalyst species. The oxirane ring-opening side reaction is particularly troublesome at the elevated temperatures encountered during normal processing, but also serves to reduce the shelf life of epoxy-functionalized silicone products.
In order to partially circumvent the gelling caused by epoxide ring-opening during the hydrosilation reaction, epoxysilicone fluids have heretofore been produced using careful control of batch temperature and olefin-epoxide feed rate during the addition reaction, and by use of low levels of mercaptans to deactivate the platinum catalyst after the completion of the hydrosilation reaction. There remains, however, the possibility that ring-opening polymerization will occur during any given batch synthesis.
Rhodium compounds are also known to catalyze the hydrosilation reaction between an SiH-functional silane or siloxane and an ethylenically unsaturated organic radicals. For example, see generally J. F. Harrod and A. J. Chalk, in "Organic Syntheses via Metal Carbonyls", Vol. 2, I. Wender and P. Pino, eds., pp. 685-687, John Wiley & Sons, New York; and J. L.Speier, Advances in Organometallic Chemistry, Vol. 17, 407 (1979). Additionally, commonly assigned U.S. Patent application entitled "Preparation of Epoxysilicon Compounds using Rhodium Catalysts", (Crivello and Fan) U.S. patent application Ser. No. 07/583,524 filed Sep. 17, 1990, Now U.S. Pat. No. 5,169,962 issued Dec. 8, 1992, discloses several rhodium catalysts suitable for use in the particular hydrosilation reaction between SiH--functional silanes or siloxanes and olefin epoxides. Also, U.S. Pat. No. 4,946,818 discloses that a rhodium colloid made by the reaction between rhodium chloride and certain silicon hydrides is an effective hydrosilation catalyst, and U.S. Pat. No. 3,928,629 discloses a process in which a rhodium sulfide or rhodium carbonyl complex is used as catalyst for organohydrogen polysiloxane-based release coatings.
Hydrosilation reactions between olefin epoxides and organohydrogensiloxanes catalyzed with platinum metal complexes containing rhodium have also been described. Reference is made to U.S. Pat. No. 4,279,717 (Eckberg) and to commonly assigned U.S. patent application Ser. Nos. 07/332,646, filed Apr. 3, 1989, and 07/473,802, filed Feb. 2, 1990.
A tertiary amine stabilizer for use with epoxy-functional silanes and siloxanes has also been previously described in the above-mentioned, commonly assigned U.S. Patent application of Crivello and Fan. In that case, a tertiary amine is added following the completion of the addition of olefin epoxide to an SiH-functionalized silicone, but prior to the stripping of volatiles from the reaction product. Thus, the tertiary amine stabilizer is not present during the addition reaction itself, such that epoxy crosslinking promoted by the elevated temperature of the addition reaction often cannot be avoided.
Due to the undesirable ring opening reaction during the hydrosilation addition, the reproducibility of the products obtained, particularly with respect to viscosity, has heretofore been less than optimal. There thus exists a need in the epoxysilicone industry for a hydrosilation reaction for the addition of epoxy-functionalized unsaturated compounds to SiH-functionalized silanes and siloxanes, in which the epoxy-ring opening is greatly suppressed or eliminated. Preferably, the epoxy ring-opening reaction would be eliminated throughout the course of the addition reaction rather than only afterwards. In such a preferred scenario, the batch-to-batch reproducibility of the end-product, as well as its shelf-life, would be substantially increased. All patents and references described herein are incorporated by reference.